Delay train for ordnance fuse

ABSTRACT

A delay train for an ordnance fuse having a body with two tandem chambers at the front end communicating via an axial bore with the main charge located in the rear end. A cup with an apertured bottom fits in the first of the tandem chambers and, except for the aperture, closes the second of the tandem chambers. A primer mix fills the cup and a delay composition fills the second chamber. Initiation of the primer mix by a firing pin is propagated via the cup aperture to the delay composition which reacts at a known slow rate, thus contributing the greater part of the time delay. Lead azide in the axial bore is initiated by the delay composition and, in turn, initiates a length of pyrocore along which the initiation is propagated to a main charge.

United States Patent Menichelli 1 Feb. 1, 1972 154] DELAY TRAIN FORORDNANCE FUSE Primary Examiner-Benjamin A. Borchelt [72] inventor.glrrfent .I. Menieheiii Panorama City, mum Exammfl .rhomas H. WebbAttorney-R. S. Sciascia and J. A. Cooke [73] Assignee: The United Statesof America as represented by the Secretary 0! the Navy ABSTRACT [22]Filed; Feb. 18, 1969 A delay train for an ordnance fuse having a bodywith two tandem chamber: at the front end communicating via an axial PIN05 800,203 bore with the main charge located in the rear end. A cupwith an apertured bottom fits in the first of the tandem chambers [52us. Cl .102/75 l02/85 |02l86.5 Chm sewn [511 int. Cl. ..F42c 9/10 F42l;v04 F 42c 1910a chamber A P'imfir mix culP a Composifion [58] dd 0Search j 85 86 5 fills the second chamber initiation of the primer mixby a firlng pin is propagated via the cup aperture to the delaycomposition which reacts at a known slow rate, thus contributing [s6]Rem-em cued the greater part of the time delay. Lead azide in the axialbore UNITED STATES PATENTS is initiated by the delay composition and, inturn, initiates a length of pyrocore along which the initiation ispropagated to 1,369,476 2Il92l Semple ...lO2/75 a main charge. 2,441,2485/l948 Morris et al. 102/865 3,i62,127 l2ll964 Breslow et al. 102/85 2Claims, 1 Drawing Figure l4 zz-g PATENTEI] FEB I I972 INVENTOR VincentJ. Menichem' BY A RNIiY DELAY TRAIN FOR ORDNANCE FUSE BACKGROUND OF THEINVENTION This invention relates generally to ordnance fuses and moreparticularly to a millisecond delay train for a fuse providing fordetonation after target penetration.

The destructiveness of projectiles fused by many presentday mechanicallyinitiated fuses is limited because projectile detonation is effected oncontact with the surface of a target. Since detonation within theinterior of the target is vastly more destructive than surfacedetonation, various attempts have been made to impose a time delaybetween projectile impact and detonation.

Mechanical timing mechanisms have been used but are usually large andbulky and often incapable of consistently and reliably providing smalltime delays, such for example, as of 50 milliseconds. Moreover, theytend to be complicated, susceptible to mechanical failure and expensive.Electronic time delays are generally satisfactory for use withelectrically initiated explosive devices, but not with mechanicallyinitiated explosive devices.

Pyrotechnic delay trains have been employed in the past and have provedgenerally satisfactory in their particular applications in largeordnance such as rockets. In this application, a large, complicated,expensive delay train is satisfactory because the percentagecontribution to the cost of the projectile is small. However, in smallcaliber ordnance which typically is expended in vast quantities, alarge, complicated and expensive design is economically prohibitive. Theparticular requirements which the instant fuse was designed to satisfyprecluded use of any of the known fuses and necessitated the researchthat culminated in this invention.

The requirement for a small, sturdy, inexpensive and reliableS-millisecond range delay train for a fuse arose because of the natureof the target and the nature of the projectile. It was found that in useagainst targets hidden in foliage or in buildings, a microsecond rangedelay known in the art did not permit sufi'lcient penetration and thedetonation was premature. Also, the projectiles for which this fuse wasdesigned were too small to accept existing fuses, and would accommodateonly a very small fuse assembly. Further, the available SO-millisecondrange delay fuses did not produce consistent delay times. Finally,existing fuses that might have been modified for the instantrequirements were prohibitively expensive for use in small caliberordnance.

One persistent problem encountered in the design of delay fuses is thebaflle between the initiator or primer and the delay composition. Thebaffle must serve four functions. Firstly, it isolates the delaycomposition column from the brisance of the primer and prevents breakupagitation, voids, compaction and other undesirable disturbance to thedesired density and distribution of the delay composition column.Secondly, the baffle prevents particles of the exploding primer frompenetrating into the delay composition column. If a par ticle were topenetrate half the length of the delay composition column, for example,the delay imposed thereby would be efiectively cut in half since thereaction would begin halfway down the column. Thirdly, the nature of thedelay composition which, although it is called gasless," in fact doesproduce a certain quantity of gas which, if not vented, will build uppressure and temperature in the delay composition chamber andunpredictably affect the rate of reaction of the delay composition.Moreover, the housing for the fuse would need to be strengthened tosupport the increased pressure, thus increasing the cost and weight. Thefourth function of the baflle is to prevent the separation of thereacting front of the delay composition column from the unreactedremainder thereof. The reaction products are in the form of a frothyslag which, if not confined, would tend to expand away from the reactingmaterial and actually cause a separation of the reacting front from thebody of the material, thereby extinguishing the reaction.

SUMMARY OF THE INVENTION Accordingly an object of this invention is toprovide a new and improved mechanically initiated, pyrotechnic, timedelay for a fuse.

Another objective of the invention is to furnish a pyrotechnic fusehaving a consistent and reliable delay in the millisecond range betweeninitiation and detonation.

Yet another object of the present invention is to provide a novelpyrotechnic time delay for a fuse that is of a suitable size for use inrelatively small caliber ordnance.

A still further object of the instant invention is to provide animproved unobturated pyrotechnic time-delay fuse with a simple designwhich is relatively inexpensive to produce.

Still another object of the invention is the provision of a rugged anddependable pyrotechnic time-delay fuse that can sustain high-impactstresses without operational failure.

Another still further object of the present invention is to provide adelay fuse in which blowby of particles of the primer into or throughthe delay composition is effectively prevented while the delaycomposition is isolated from primer brisance, constrained from unwantedexpansion and vented from pressure increase.

Briefly, in accordance with this invention, these and other objects areattained by providing an explosive train for a fuse wherein two axiallyaligned chambers separated by an aper tured base of a cup fixedlysecured in the upper chamber. The cup contains a primer mixture and thelower chamber contains a delay composition. The apertured base serves asa baffle between the primer mixture and delay composition and also tovent the lower chamber.

DESCRIPTION OF THE DRAWING A more complete appreciation of the inventionand its many attendant advantages will develop as it becomes better undelstood by reference to the following detailed description whenconsidered in connection with the solitary FIGURE of the drawing, whichis an elevational, partly sectional view, of a preferred embodiment ofthe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, thefuse is embodied in a generally cylindrical body 10 which may be securedin a shell, grenade, bomb or other explosive projectile, usually in itshose and directly in line or alignable with a firing pin 12. The body issecured in the projectile in any appropriate manner, such as in anarming rotor or fixed in line with arming drop leaves, for example.

A frontal chamber 14 is formed in the forward portion of body 10 havinggenerally cylindrical walls and extending axi ally into the body aboutone third of its length. Adjacent to the frontal chamber and axiallyaligned therewith is a generally cylindrical central chamber 16extending axially into the body and having an axial depth and across-sectional diameter both somewhat less than the correspondingdimensions of the frontal chamber. An axial bore 18 is formed in body 10to provide communication between the bottom of the central chamber andthe rear end of the fuse body.

A cylindrical bafile cup 20 having a diameter substantially the same asthe frontal chamber fits snugly therein and rests against the shoulder22 formed at the junction of the two chambers by the difference indiameters thereof. An axial aperture 24 is formed through the bottom, orbaseplate, of cup 20 provides communication between the interior of thecup 20 and the central chamber 16.

Overlying the top edge 26 of the cup 20 and covering the open topthereof is a frangible disc 28 of any suitable material, such as thinsteel or aluminum. The entire top edge of body it) is crimped inwardlyat 30 over the peripheral edge of the disc 2!, thereby securely clampingthe disc against the top edge 26 of the cup sidewall and effectingthereby a secure seal of the cup. The inward crimp 30 is also effectiveto hold the bottom edge of the cup 20 securely against the shoulder 22,thereby preventing any relative motion, or play of the cup 20 within thefrontal chamber 14.

The cup is filled with a suitable primer mix 32 such, for example, as 33percent potassium chlorate, 33 percent antimony sulfide, 28 percent leadazide and 6 percent carborundum, which will be initiated when the firingpin 12 stabs through the frangible disc 28. The aperture 24 may befilled with the primer mix, a suitable igniter, or it may remain empty.

The central chamber 16 is filled with a suitable delay composition 34such, for example, as 49 percent tungsten, 41 percent barium chromate,percent potassium perchlorate and 5 percent diatomaceous earth, whichmay be initiated by the primer mix via the aperture 24. The delaycomposition 34 reacts at a known constant rate, contributing the greaterpart of the time delay and then initiates the contents of the axial bore18 which may be lead azide and, either directly or by way of anintervening pyrocore, initiates the main charge of an ordnance device.

The success of this small, simple, stab-initiated unobturatedmillisecond range delay train for a fuse in achieving consistent andreliable delay times, pomible in the past only by complicated,cumbersome and expensive designs, is believed to be largely achieved bythe cup 20 and its support and securement within the body. The form ofthe baffle cup 20 inherently prevents blowby of particles of explodingprimer around the edge of the baffle. The small aperture 24 in the cupbottom, or baseplate, pennits initiation of the delay composition in thecentral chamber and also permits venting of gases therefrom, yet issufficiently small to enable the cup bottom to shield the compositionfrom the brisance of the exploding primer and to prevent excessexpansion of the delay composition reaction products and reaction frontaway from the remaining unreacted composition. This cooperativecombination of cup, aperture and body efficaciously performs all thefunctions of the baffle and does it simply, inexpensively and reliably.

The delay time of the fuse may be shortened by partially filling thecentral chamber 16 with a fast reacting substance, such as lead azide,and then filling the remainder of the central chamber with the delaycomposition. The delay time is thereby adjustable, within certainlimits, when the fuze is assembled. Also, the percentages of thecomponents of the delay composition may be altered to produce differentrates of reaction.

Obviously numerous other variations and modifications of theabove-described best mode or preferred embodiment of the invention,defined in the claims, may be made in light of the above teachings.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

l. A delay train for a mechanical fuse comprising:

a body having defined therein adjacent frontal and central chambers, thefrontal chamber opening to the front of said body and the centralchamber opening to the rear of said frontal chamber, and a passageleading from the rear of said central chamber to the exterior of saidbody;

a cup having sidewalls and a bottom secured in the frontal chamber ofsaid body;

said cup bottom having an aperture defined therethrough and coveringsaid central chamber,

a frangible disc secured in said body and covering said frontal chamber;

a primer mix disposed in said cup and in its aperture and initiatable bya firing pin penetrating the frangible disc;

a delay composition completely filling said central chamber whereby saiddelay composition is contiguous with and initiatable by said primer mixvia said aperture; and

a pyrotechnic composition disposed in said passage initiatable by saiddelay composition and by way of which the initiation is propagated to amain charge.

2. A stab-initiated, millisecond range, pyrotechnic timedelay fusecomprising:

a generally cylindrical body having a front end and a rear end andhaving defined therein at least two chambers and an axial bore;

the first of said chambers communicating with the front end of saidbody;

the second of said chambers to the rear of and contiguous to said firstchamber and communicating therewith;

said axial bore communicating between said second chamber and said bodyrear end;

said first chamber containing a baffle cup having a sidewall and anapertured baseplate, the cross-sectional dimension of said cup beingsubstantially the same as the cross-sectional dimension of said firstchamber;

said second chamber cross-sectional dimension being less than said firstchamber cross-sectional dimension so that a front facing shoulder isformed between said first and second chambers;

said cup baseplate resting on said shoulder and securely heldthereagainst by said sidewalls;

a frangible disc of substantially the same dimension as thecross-sectional dimension of said first chamber and positioned thereinand overlying the top edge of said cup sidewall;

said body front end being crimped over said disc and said cup sidewalltop edge, whereby said disc is securely clamped over and covering themouth of said cup and said cup is securely fixed in position againstsaid shoulder;

said cup and its aperture containing a primer initiable by the stab ofthe firing pin through said frangible disc and into said primer;

said second chamber being completely filled with a delay compositionwhereby said delay composition is contiguous with and initiatable bysaid primer via said aperture, said delay composition having a reactionrate substantially slower than the reaction rate of said primer;

said axial bore containing a pyrotechnic material contiguous with andinitiatable by said delay composition and having a reaction ratesubstantially faster than said delay composition reaction rate.

1. A delay train for a mechanical fuse comprising: a body having definedtherein adjacent frontal and central chambers, the frontal chamberopening to the front of said body and the central chamber opening to therear of said frontal chamber, and a passage leading from the rear ofsaid central chamber to the exterior of said body; a cup havingsidewalls and a bottom secured in the frontal chamber of said body; saidcup bottom having an aperture defined therethrough and covering saidcentral chamber, a frangible disc secured in said body and covering saidfrontal chamber; a primer mix disposed in said cup and in its apertureand initiatable by a firing pin penetrating the frangible disc; a delaycomposition completely filling said central chamber whereby said delaycomposition is contiguous with and initiatable by said primer mix viasaid aperture; and a pyrotechnic composition disposed in said passageinitiatable by said delay composition and by way of which the initiationis propagated to a main charge.
 2. A stab-initiated, millisecond range,pyrotechnic time-delay fuse comprising: a generally cylindrical bodyhaving a front end and a rear end and having defined therein at leasttwo chambers and an axial bore; the first of said chambers communicatingwith the front end of said body; the second of said chambers to the rearof and contiguous to said first chamber and communicating therewith;said axial bore communicating between said second chamber and said bodyrear end; said first chamber containing a baffle cup having a sidewalland an apertured baseplate, the cross-sectional dimension of said cupbeing substantially the same as the cross-sectional dimension of saidfirst chamber; said second chamber cross-sectional dimension being lessthan said first chamber cross-sectional dimension so that a front facingshoulder is formed between said first and second chambers; said cupbaseplate resting on said shoulder and securely held thereagainst bysaid sidewalls; a frangible disc of substantially the same dimension asthe cross-sectional dimension of said first chamber and positionedtherein and overlying the top edge of said cup sidewall; said body frontend being crimped over said disc and said cup sidewall top edge, wherebysaid disc is securely clamped over and covering the mouth of said cupand said cup is securely fixed in position against said shoulder; saidcup and its aperture containing a primer initiable by the stab of thefiring pin through said frangible disc and into said primer; said secondchamber being completely filled with a delay composition whereby saiddelay composition is contiguous with and initiatable by said primer viasaid aperture, said delay composition having a reaction ratesubstantially slower than the reaction rate of said primer; said axialbore containing a pyrotechnic material contiguous with and initiatableby said delay composition and having a reaction rate substantiallyfaster than said delay composition reaction rate.